Preheat the oven to 325°F (165°C). Prepare two 9x5-inch loaf pans by greasing and lining them with parchment paper.
In a medium bowl, whisk together the flour, baking powder, and salt.
In a large mixing bowl, cream the butter and shortening until light and fluffy. Gradually add the sugar, beating well after each addition.
Beat in the eggs, one at a time. Add vanilla and chocolate extract, mixing until combined.
Alternately add the dry ingredients and buttermilk, mixing just until incorporated after each addition.
Fold in the chopped chocolate and cocoa powder.
Divide the batter between the prepared pans and smooth the tops.
Bake for 40 minutes, then add a pan of water in the oven and continue baking for another 20 minutes, or until a toothpick comes out clean.
Let the cakes cool in the pans for 10 minutes before transferring to a wire rack to cool completely.
Optional: Top with chocolate glaze or powdered sugar before serving.